Specialized tip/stalk-like and phalanx-like endothelial cells from embryonic stem cells

Angiogenesis is promoted by hypoxic cervical carcinoma-derived extracellular vesicles depending on the endothelial cell environment

INTRODUCTION

Cancer needs perfusion for its growth and metastasis. Cancer cell-derived extracellular vesicles (CA-EVs) alter the tumor microenvironment (TME), potentially promoting angiogenesis. We hypothesize that conditions in the tumor, e.g., hypoxia, and in the target cells of the TME, e.g., nutrient deprivation or extracellular matrix, can affect the angiogenic potential of CA-EVs, which would contribute to explaining the regulation of tumor vascularization and its influence on cancer growth and metastasis.

METHODS

CA-EVs were isolated and characterized from cervical carcinoma cell lines HeLa and SiHa cultured under normoxia and hypoxia, and their angiogenic potential was evaluated in vitro in three endothelial cells (ECs) lines and aortic rings, cultured in basal (growth factor-reduced) or complete medium.

RESULTS

Hypoxia increased EV production 10-100 times and protein content 2-4 times compared to normoxic CA-EVs. HeLa-EVs contained six times more RNA than SiHa-EVs, and this concentration was not affected by hypoxia. Treatment with CA-EVs increased tube formation and sprouting in ECs and aortic rings cultured in basal medium and long-term stabilized the stablished vascular networks formed by ECs cultured in complete medium.

CONCLUSION

Hypoxia differentially affects CA-EVs in a cell line-dependent manner. The cellular environment (nutrient availability and extracellular matrix scaffold) influences the effect of CA-EV on the angiogenic potential of ECs.

Review and comparative analysis of machine learning-based predictors for predicting and analyzing of anti-angiogenic peptides

Cancer is one of the leading causes of death worldwide and underlying this is angiogenesis that represents one of the hallmarks of cancer. Ongoing effort is already under way in the discovery of anti-angiogenic peptides (AAPs) as a promising therapeutic route by tackling the formation of new blood vessels. As such, the identification of AAPs constitutes a viable path for understanding their mechanistic properties pertinent for the discovery of new anti-cancer drugs. In spite of the abundance of peptide sequences in public databases, experimental efforts in the identification of anti-angiogenic peptides have progressed very slowly owing to its high expenditures and laborious nature. Owing to its inherent ability to make sense of large volumes of data, machine learning (ML) represents a lucrative technique that can be harnessed for peptide-based drug discovery. In this review, we conducted a comprehensive and comparative analysis of ML-based AAP predictors in terms of their employed feature descriptors, ML algorithms, cross-validation methods and prediction performance. Moreover, the common framework of these AAP predictors and their inherent weaknesses are also discussed. Particularly, we explore future perspectives for improving the prediction accuracy and model interpretability, which represents an interesting avenue for overcoming some of the inherent weaknesses of existing AAP predictors. We anticipate that this review would assist researchers in the rapid screening and identification of promising AAPs for clinical use.

Treatment of pyogenic granuloma with copper vapor laser radiation

Background. Pyogenic granuloma (PG) or lobular capillary hemangioma, ICD10 code: L98.0. appears as a single bright red or violet papule up to 20 mm in size, on the face, fingers, skull surface, arms, and intergluteal fold, as well as on the oral mucous membranes. Surgical removal of facial PG is not always possible due to insufficient thickness of the dermis. Treatment of PG with a pulsed dye laser (PDL) or neodymium laser (Nd:YAG) can achieve a noticeable elimination of the lesion but is reported to be accompanied by such side effects as purpura or scarring. It determines the feasibility of introducing into clinical practice the methods of laser treatment of PG using the radiation of a copper vapor laser (CVL) with a wavelength of 578 nm, which effectively absorbed by the blood. Aim. The assessment of the clinical efficacy and safety of the CVL treating PG. Methods. 26 adult patients with PG in various parts of the face, including the lips, limbs, and trunk, were included in this study. PG treatment was carried out in one session with CVL (Yakhroma-Med, FIAN) at an average power of 0.71.0 W, at a wavelength of 578 nm, exposure time 0.20.3 s. The diameter of the light spot is 1 mm. Results. Immediately after the single laser treatment, the PG involved area became grey. In 710 days, the irradiated area was utterly similar to the adjacent intact skin. No postoperative bleeding or infection was noted. Side effects included mild skin atrophy. During the follow-up observation for five years, no side effects were found. Conclusion. The high efficiency of PG elimination using CVL in the absence of pronounced side effects allows suggesting this method for introducing into dermatologists and cosmetologists' clinical practice as a highly effective and inexpensive method of treatment.

Endothelial Cell Glucose Metabolism and Angiogenesis

Angiogenesis, a process of new blood vessel formation from the pre-existing vascular bed, is a critical event in various physiological and pathological settings. Over the last few years, the role of endothelial cell (EC) metabolism in angiogenesis has received considerable attention. Accumulating studies suggest that ECs rely on aerobic glycolysis, rather than the oxidative phosphorylation pathway, to produce ATP during angiogenesis. To date, numerous critical regulators of glucose metabolism, fatty acid oxidation, and glutamine metabolism have been identified to modulate the EC angiogenic switch and pathological angiogenesis. The unique glycolytic feature of ECs is critical for cell proliferation, migration, and responses to environmental changes. In this review, we provide an overview of recent EC glucose metabolism studies, particularly glycolysis, in quiescent and angiogenic ECs. We also summarize and discuss potential therapeutic strategies that take advantage of EC metabolism. The elucidation of metabolic regulation and the precise underlying mechanisms could facilitate drug development targeting EC metabolism to treat angiogenesis-related diseases.

Pericyte migration and proliferation are tightly synchronized to endothelial cell sprouting dynamics

Pericytes are critical for microvascular stability and maintenance, among other important physiological functions, yet their involvement in vessel formation processes remains poorly understood. To gain insight into pericyte behaviors during vascular remodeling, we developed two complementary tissue explant models utilizing 'double reporter' animals with fluorescently-labeled pericytes and endothelial cells (via Ng2:DsRed and Flk-1:eGFP genes, respectively). Time-lapse confocal imaging of active vessel remodeling within adult connective tissues and embryonic skin revealed a subset of pericytes detaching and migrating away from the vessel wall. Vessel-associated pericytes displayed rapid filopodial sampling near sprouting endothelial cells that emerged from parent vessels to form nascent branches. Pericytes near angiogenic sprouts were also more migratory, initiating persistent and directional movement along newly forming vessels. Pericyte cell divisions coincided more frequently with elongating endothelial sprouts, rather than sprout initiation sites, an observation confirmed with in vivo data from the developing mouse brain. Taken together, these data suggest that (i) pericyte detachment from the vessel wall may represent an important physiological process to enhance endothelial cell plasticity during vascular remodeling, and (ii) pericyte migration and proliferation are highly synchronized with endothelial cell behaviors during the coordinated expansion of a vascular network.

Angiogenesis in gynecological cancers and the options for anti-angiogenesis therapy

Angiogenesis is required in cancer, including gynecological cancers, for the growth of primary tumors and secondary metastases. Development of anti-angiogenesis therapy in gynecological cancers and improvement of its efficacy have been a major focus of fundamental and clinical research. However, survival benefits of current anti-angiogenic agents, such as bevacizumab, in patients with gynecological cancer, are modest. Therefore, a better understanding of angiogenesis and the tumor microenvironment in gynecological cancers is urgently needed to develop more effective anti-angiogenic therapies, either or not in combination with other therapeutic approaches. We describe the molecular aspects of (tumor) blood vessel formation and the tumor microenvironment and provide an extensive clinical overview of current anti-angiogenic therapies for gynecological cancers. We discuss the different phenotypes of angiogenic endothelial cells as potential therapeutic targets, strategies aimed at intervention in their metabolism, and approaches targeting their (inflammatory) tumor microenvironment.

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.

A Computational Model of the Endothelial to Mesenchymal Transition

Endothelial cells (ECs) form the lining of lymph and blood vessels. Changes in tissue requirements or wounds may cause ECs to behave as tip or stalk cells. Alternatively, they may differentiate into mesenchymal cells (MCs). These processes are known as EC activation and endothelial-to-mesenchymal transition (EndMT), respectively. EndMT, Tip, and Stalk EC behaviors all require SNAI1, SNAI2, and Matrix metallopeptidase (MMP) function. However, only EndMT inhibits the expression of VE-cadherin, PECAM1, and VEGFR2, and also leads to EC detachment. Physiologically, EndMT is involved in heart valve development, while a defective EndMT regulation is involved in the physiopathology of cardiovascular malformations, congenital heart disease, systemic and organ fibrosis, pulmonary arterial hypertension, and atherosclerosis. Therefore, the control of EndMT has many promising potential applications in regenerative medicine. Despite the fact that many molecular components involved in EC activation and EndMT have been characterized, the system-level molecular mechanisms involved in this process have not been elucidated. Toward this end, hereby we present Boolean network model of the molecular involved in the regulation of EC activation and EndMT. The simulated dynamic behavior of our model reaches fixed and cyclic patterns of activation that correspond to the expected EC and MC cell types and behaviors, recovering most of the specific effects of simple gain and loss-of-function mutations as well as the conditions associated with the progression of several diseases. Therefore, our model constitutes a theoretical framework that can be used to generate hypotheses and guide experimental inquiry to comprehend the regulatory mechanisms behind EndMT. Our main findings include that both the extracellular microevironment and the pattern of molecular activity within the cell regulate EndMT. EndMT requires a lack of VEGFA and sufficient oxygen in the extracellular microenvironment as well as no FLI1 and GATA2 activity within the cell. Additionally Tip cells cannot undergo EndMT directly. Furthermore, the specific conditions that are sufficient to trigger EndMT depend on the specific pattern of molecular activation within the cell.

Differentiation and expansion of endothelial cells requires pre-optimization of KDR+ expression kinetics

Human endothelial cells (ECs) are important tools in research and development of new therapies in the fields of angiogenesis, vasculogenesis, engineering organoids and multicellular tissues, drug discovery, and disease modeling. Efficient and robust induction of ECs from human pluripotent stem cells (hPSCs) serve as a renewable and indefinite cell sources. However, individual lines of embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) are distinct and can often respond very differently to the same microenvironmental cues. Therefore, we set out to develop a differentiation methodology specifically designed for robustness across multiple human iPSC lines. In general, the key soluble signals remain consistent across cell lines, but because the differentiation and proliferation kinetics can differ slightly in hESC and iPSC cell lines, the time point for KDR+ cell sorting must be pre-determined for each cell line. This three-stage induction method uses three different chemically defined medium formulations and generates highly purified populations of actively proliferating and functional VE-cadherin+ ECs within 30 days.

Interferon-Gamma and Tumor Necrosis Factor-Related Weak Inducer of Apoptosis Expression in Neoangiogenesis in Colorectal Polypoid Lesions

BACKGROUND

Interferon gamma (IFNγ) and tumor necrosis factor-related weak inducer of apoptosis (TWEAK) molecules seem to have a potential effect on angiogenic factors such as vascular endothelial growth factor (VEGF). The aim of this study was to assess a possible interplay between IFNγ and TWEAK cytokines and VEGF machinery in the different steps of colorectal carcinogenesis.

METHODS

A total of 92 subjects with colonic adenoma or cancer who underwent screening colonoscopy or surgery were prospectively enrolled. Polypoid lesion tissue samples were collected and frozen. Real-time reverse transcription polymerase chain reaction for IFNγ, TWEAK, and VEGF-A mRNA expression was performed. Immunoassays for VEGF-A, VEGF-C, VEGFR-1, VEGFR-2, and VEGFR-3 were also performed. Nonparametric statistics, receiver operating characteristic curve analysis, and logistic multiple regression analysis were used.

RESULTS

IFNγ and TWEAK mRNA expression was higher in patients with T2 or more advanced colorectal cancer than in those with adenomas or T1 cancer (p < 0.001 and p = 0.01, respectively). IFNγ and TWEAK mRNA expression levels directly correlated with VEGF-A mRNA expression levels (rho = 0.44, p < 0.001 and rho = 0.29, p = 0.004, respectively). On the contrary, IFNγ and TWEAK mRNA expression levels inversely correlated with VEGF-C protein levels (rho = -0.29, p = 0.04 and rho = -0.31, p = 0.03, respectively). Similarly, IFNγ and TWEAK mRNA expression levels inversely correlated with VEGFR2 protein levels (rho = -0.38, p = 0.033 and rho = -0.40, p = 0.025, respectively).

CONCLUSION

This study showed that in colorectal polypoid lesions, IFNγ and TWEAK expressions are directly correlated to VEGF-A expression but inversely correlated with VEGFR2 levels, suggesting a possible feedback mechanism in the regulation of VEGF-A expression.

Phenotypic characteristics of human bone marrow-derived endothelial progenitor cells in vitro support cell effectiveness for repair of the blood-spinal cord barrier in ALS

Amyotrophic lateral sclerosis (ALS) was recently recognized as a neurovascular disease. Accumulating evidence demonstrated blood-spinal-cord barrier (BSCB) impairment mainly via endothelial cell (EC) degeneration in ALS patients and animal models. BSCB repair may be a therapeutic approach for ALS. We showed benefits of human bone marrow endothelial progenitor cell (hBMEPC) transplantation into symptomatic ALS mice on barrier restoration; however, cellular mechanisms remain unclear. The study aimed to characterize hBMEPCs in vitro under normogenic conditions. hBMEPCs were cultured at different time points. Enzyme-linked immunosorbent assay (ELISA) was used to detect concentrations of angiogenic factors (VEGF-A, angiogenin-1, and endoglin) and angiogenic inhibitor endostatin in conditioned media. Double immunocytochemical staining for CD105, ZO-1, and occludin with F-actin was performed. Results showed predominantly gradual significant post-culture increases of VEGF-A and angiogenin-1 levels. Cultured cells displayed distinct rounded or elongated cellular morphologies and positively immunoexpressed for CD105, indicating EC phenotype. Cytoskeletal F-actin filaments were re-arranged according to cell morphologies. Immunopositive expressions for ZO-1 were detected near inner cell membrane and for occludin on cell membrane surface of adjacent hBMEPCs. Together, secretion of angiogenic factors by cultured cells provides evidence for a potential mechanism underlying endogenous EC repair in ALS through hBMEPC transplantation, leading to restored barrier integrity. Also, ZO-1 and occludin immunoexpressions, confirming hBMEPC interactions in vitro, may reflect post-transplant cell actions in vivo.

Cellular and Molecular Heterogeneity Associated with Vessel Formation Processes

The microvasculature heterogeneity is a complex subject in vascular biology. The difficulty of building a dynamic and interactive view among the microenvironments, the cellular and molecular heterogeneities, and the basic aspects of the vessel formation processes make the available knowledge largely fragmented. The neovascularisation processes, termed vasculogenesis, angiogenesis, arteriogenesis, and lymphangiogenesis, are important to the formation and proper functioning of organs and tissues both in the embryo and the postnatal period. These processes are intrinsically related to microvascular cells, such as endothelial and mural cells. These cells are able to adjust their activities in response to the metabolic and physiological requirements of the tissues, by displaying a broad plasticity that results in a significant cellular and molecular heterogeneity. In this review, we intend to approach the microvasculature heterogeneity in an integrated view considering the diversity of neovascularisation processes and the cellular and molecular heterogeneity that contribute to microcirculatory homeostasis. For that, we will cover their interactions in the different blood-organ barriers and discuss how they cooperate in an integrated regulatory network that is controlled by specific molecular signatures.

Tumor angiogenesis and anti-angiogenic gene therapy for cancer

When Folkman first suggested a theory about the association between angiogenesis and tumor growth in 1971, the hypothesis of targeting angiogenesis to treat cancer was formed. Since then, various studies conducted across the world have additionally confirmed the theory of Folkman, and numerous efforts have been made to explore the possibilities of curing cancer by targeting angiogenesis. Among them, anti-angiogenic gene therapy has received attention due to its apparent advantages. Although specific problems remain prior to cancer being fully curable using anti-angiogenic gene therapy, several methods have been explored, and progress has been made in pre-clinical and clinical settings over previous decades. The present review aimed to provide up-to-date information concerning tumor angiogenesis and gene delivery systems in anti-angiogenic gene therapy, with a focus on recent developments in the study and application of the most commonly studied and newly identified anti-angiogenic candidates for anti-angiogenesis gene therapy, including interleukin-12, angiostatin, endostatin, tumstatin, anti-angiogenic metargidin peptide and endoglin silencing.

Functional comparison of distinct Brachyury+ states in a renal differentiation assay

Mesodermal populations can be generated in vitro from mouse embryonic stem cells (mESCs) using three-dimensional (3-D) aggregates called embryoid bodies or two-dimensional (2-D) monolayer culture systems. Here, we investigated whether Brachyury-expressing mesodermal cells generated using 3-D or 2-D culture systems are equivalent or, instead, have different properties. Using a Brachyury-GFP/E2-Crimson reporter mESC line, we isolated Brachyury-GFP ⁺ mesoderm cells using flow-activated cell sorting and compared their gene expression profiles and ex vivo differentiation patterns. Quantitative real-time polymerase chain reaction analysis showed significant up-regulation of Cdx2, Foxf1 and Hoxb1 in the Brachyury-GFP⁺ cells isolated from the 3-D system compared with those isolated from the 2-D system. Furthermore, using an ex vivo mouse kidney rudiment assay, we found that, irrespective of their source, Brachyury-GFP⁺ cells failed to integrate into developing nephrons, which are derived from the intermediate mesoderm. However, Brachyury-GFP⁺ cells isolated under 3-D conditions appeared to differentiate into endothelial-like cells within the kidney rudiments, whereas the Brachyury-GFP⁺ isolated from the 2-D conditions only did so to a limited degree. The high expression of Foxf1 in the 3-D Brachyury-GFP⁺ cells combined with their tendency to differentiate into endothelial-like cells suggests that these mesodermal cells may represent lateral plate mesoderm.

Co-Emergence of Specialized Endothelial Cells from Embryonic Stem Cells

A well-formed and robust vasculature is critical to the health of most organ systems in the body. However, the endothelial cells (ECs) forming the vasculature can exhibit a number of distinct functional subphenotypes like arterial or venous ECs, as well as angiogenic tip and stalk ECs. In this study, we investigate the in vitro differentiation of EC subphenotypes from embryonic stem cells (ESCs). Using our staged induction methods and chemically defined mediums, highly angiogenic EC subpopulations, as well as less proliferative and less migratory EC subpopulations, are derived. Furthermore, the EC subphenotypes exhibit distinct surface markers, gene expression profiles, and positional affinities during sprouting. While both subpopulations contained greater than 80% VE-cad⁺/CD31⁺ cells, the tip/stalk-like EC contained predominantly Flt4⁺/Dll4⁺/CXCR4⁺/Flt-1^- cells, while the phalanx-like EC was composed of higher numbers of Flt-1⁺ cells. These studies suggest that the tip-specific EC can be derived in vitro from stem cells as a distinct and relatively stable EC subphenotype without the benefit of its morphological positioning in the sprouting vessel.

A Network Model to Explore the Effect of the Micro-environment on Endothelial Cell Behavior during Angiogenesis

Angiogenesis is an important adaptation mechanism of the blood vessels to the changing requirements of the body during development, aging, and wound healing. Angiogenesis allows existing blood vessels to form new connections or to reabsorb existing ones. Blood vessels are composed of a layer of endothelial cells (ECs) covered by one or more layers of mural cells (smooth muscle cells or pericytes). We constructed a computational Boolean model of the molecular regulatory network involved in the control of angiogenesis. Our model includes the ANG/TIE, HIF, AMPK/mTOR, VEGF, IGF, FGF, PLCγ/Calcium, PI3K/AKT, NO, NOTCH, and WNT signaling pathways, as well as the mechanosensory components of the cytoskeleton. The dynamical behavior of our model recovers the patterns of molecular activation observed in Phalanx, Tip, and Stalk ECs. Furthermore, our model is able to describe the modulation of EC behavior due to extracellular micro-environments, as well as the effect due to loss- and gain-of-function mutations. These properties make our model a suitable platform for the understanding of the molecular mechanisms underlying some pathologies. For example, it is possible to follow the changes in the activation patterns caused by mutations that promote Tip EC behavior and inhibit Phalanx EC behavior, that lead to the conditions associated with retinal vascular disorders and tumor vascularization. Moreover, the model describes how mutations that promote Phalanx EC behavior are associated with the development of arteriovenous and venous malformations. These results suggest that the network model that we propose has the potential to be used in the study of how the modulation of the EC extracellular micro-environment may improve the outcome of vascular disease treatments.

Microfibrous Scaffolds Enhance Endothelial Differentiation and Organization of Induced Pluripotent Stem Cells

INTRODUCTION

Human induced pluripotent stem cells (iPSCs) are a promising source of endothelial cells (iPSC-ECs) for engineering three-dimensional (3D) vascularized cardiac tissues. To mimic cardiac microvasculature, in which capillaries are oriented in parallel, we hypothesized that endothelial differentiation of iPSCs within topographically aligned 3D scaffolds would be a facile one-step approach to generate iPSC-ECs as well as induce aligned vascular organization.

METHODS

Human iPSCs underwent endothelial differentiation within electrospun 3D polycaprolactone (PCL) scaffolds having either randomly oriented or parallel-aligned microfibers. Using transcriptional, protein, and endothelial functional assays, endothelial differentiation was compared between conventional two-dimensional (2D) films and 3D scaffolds having either randomly oriented or aligned microfibers. Furthermore, the role of parallel-aligned microfiber patterning on the organization of vessel-like networks was assessed.

RESULTS

The cells in both the randomly oriented and aligned 3D scaffolds demonstrated an 11-fold upregulation in gene expression of the endothelial phenotypic marker, CD31, compared to cells on 2D films. This upregulation corresponded to >3-fold increase in CD31 protein expression in 3D scaffolds, compared to 2D films. Concomitantly, other endothelial phenotypic markers including CD144 and endothelial nitric oxide synthase also showed significant transcriptional upregulation in 3D scaffolds by >7-fold, compared to 2D films. Nitric oxide production, which is characteristic of endothelial function, was produced 4-fold more abundantly in 3D scaffolds, compared to on 2D PCL films. Within aligned scaffolds, the iPSC-ECs displayed parallel-aligned vascular-like networks with 70% longer branch length, compared to cells in randomly oriented scaffolds, suggesting that fiber topography modulates vascular network-like formation and patterning.

CONCLUSION

Together, these results demonstrate that 3D scaffold structure promotes endothelial differentiation, compared to 2D substrates, and that aligned topographical patterning induces anisotropic vascular network organization.

Induced Pluripotent Stem Cell-Derived Endothelial Cells in Insulin Resistance and Metabolic Syndrome

Insulin resistance leads to a number of metabolic and cellular abnormalities including endothelial dysfunction that increase the risk of vascular disease. Although it has been particularly challenging to study the genetic determinants that predispose to abnormal function of the endothelium in insulin-resistant states, the possibility of deriving endothelial cells from induced pluripotent stem cells generated from individuals with detailed clinical phenotyping, including accurate measurements of insulin resistance accompanied by multilevel omic data (eg, genetic and genomic characterization), has opened new avenues to study this relationship. Unfortunately, several technical barriers have hampered these efforts. In the present review, we summarize the current status of induced pluripotent stem cell-derived endothelial cells for modeling endothelial dysfunction associated with insulin resistance and discuss the challenges to overcoming these limitations.

Multifactorial Optimizations for Directing Endothelial Fate from Stem Cells

Embryonic stem cells (ESC) and induced pluripotent stem (iPS) cells are attractive in vitro models of vascular development, therapeutic angiogenesis, and tissue engineering. However, distinct ESC and iPS cell lines respond differentially to the same microenvironmental factors. Developing improved/optimized differentiation methodologies tailored/applicable in a number of distinct iPS and ESC lines remains a challenge in the field. Currently published methods for deriving endothelial cells (EC) robustly generate high numbers of endothlelial progenitor cells (EPC) within a week, but their maturation to definitive EC is much more difficult, taking up to 2 months and requiring additional purification. Therefore, we set out to examine combinations/levels of putative EC induction factors—utilizing our stage-specific chemically-defined derivation methodology in 4 ESC lines including: kinetics, cell seeding density, matrix signaling, as well as medium treatment with vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF). The results indicate that temporal development in both early and late stages is the most significant factor generating the desired cells. The generation of early Flk-1⁺/KDR⁺ vascular progenitor cells (VPC) from pluripotent ESC is directed predominantly by high cell seeding density and matrix signaling from fibronectin, while VEGF supplementation was NOT statistically significant in more than one cell line, especially with fibronectin matrix which sequesters autocrine VEGF production by the differentiating stem cells. Although some groups have shown that the GSK3-kinase inhibitor (CHIR) can facilitate EPC fate, it hindered the generation of KDR+ cells in our preoptimized medium formulations. The methods summarized here significantly increased the production of mature vascular endothelial (VE)-cadherin+ EC, with up to 93% and 57% purity from mouse and human ESC, respectively, before VE-cadherin+ EC purification.

Identifying Behavioral Phenotypes and Heterogeneity in Heart Valve Surface Endothelium

Heart valvular endothelial cells (VECs) are distinct from vascular endothelial cells (ECs), but have an uncertain context within the spectrum of known endothelial phenotypes, including lymphatic ECs (LECs). Profiling the phenotypes of the heart valve surface VECs would facilitate identification of a proper seeding population for tissue-engineered valves, as well as elucidate mechanisms of valvular disease. Porcine VECs and porcine aortic ECs (AECs) were isolated from pig hearts and characterized to assess known EC and LEC markers. A transwell migration assay determined their propensity to migrate toward vascular endothelial growth factor, an angiogenic stimulus, over 24 h. Compared to AECs, Flt-1 was expressed on almost double the percentage of VECs, measured as 74 versus 38%. The expression of angiogenic EC markers CXCR4 and DLL4 was >90% on AECs, whereas VECs showed only 35% CXCR4+ and 47% DLL4+. AECs demonstrated greater migration (71.5 ± 11.0 cells per image field) than the VECs with 30.0 ± 15.3 cells per image field (p = 0.032). In total, 30% of VECs were positive for LYVE1+/Prox1+, while these markers were absent in AECs. In conclusion, the population of cells on the surface of heart valves is heterogeneous, consisting largely of nonangiogenic VECs and a subset of LECs. Previous studies have indicated the presence of LECs within the interior of the valves; however, this is the first study to demonstrate their presence on the surface. Identification of this unique endothelial mixture is a step forward in the development of engineered valve replacements as a uniform EC seeding population may not be the best option to maximize transplant success.

Endothelial cells expressing low levels of CD143 (ACE) exhibit enhanced sprouting and potency in relieving tissue ischemia

The sprouting of endothelial cells from pre-existing blood vessels represents a critical event in the angiogenesis cascade. However, only a fraction of cultured or transplanted endothelial cells form new vessels. Moreover, it is unclear whether this results from a stochastic process or instead relates to certain endothelial cells having a greater angiogenic potential. This study investigated whether there exists a sub-population of cultured endothelial cells with enhanced angiogenic potency in vitro and in vivo. First, endothelial cells that participated in sprouting, and non-sprouting cells, were separately isolated from a 3D fibrin gel sprouting assay. Interestingly, the sprouting cells, when placed back into the same assay, displayed a sevenfold increase in the number of sprouts, as compared to control cells. Angiotensin-converting enzyme (CD143) was significantly down regulated on sprouting cells, as compared to regular endothelial cells. A subset of endothelial cells with low CD143 expression was then prospectively isolated from an endothelial cell culture. Finally, these cells were found to have greater potency in alleviating local ischemia, and restoring regional blood perfusion when transplanted into ischemic hindlimbs, as compared to unsorted endothelial cells. In summary, this study indicates that low expression of CD143 can be used as a biomarker to identify an endothelial cell sub-population that is more capable to drive neovascularization.

Chemotaxis of human induced pluripotent stem cell-derived endothelial cells

This study examined the homing capacity of human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) and their response to chemotactic gradients of stromal derived factor-1α (SDF). We have previously shown that EC derived from murine pluripotent stem cells can home to the ischemic hindlimb of the mouse. In the current study, we were interested to understand if ECs derived from human induced pluripotent stem cells are capable of homing. The homing capacity of iPSC-ECs was assessed after systemic delivery into immunodeficient mice with unilateral hindlimb ischemia. Furthermore, the iPSC-ECs were evaluated for their expression of CXCR4 and their ability to respond to SDF chemotactic gradients in vitro. Upon systemic delivery, the iPSC-ECs transiently localized to the lungs but did not home to the ischemic limb over the course of 14 days. To understand the mechanism of the lack of homing, the expression levels of the homing receptor, CXCR4, was examined at the transcriptional and protein levels. Furthermore, their ability to migrate in response to chemokines was assessed using microfluidic and scratch assays. Unlike ECs derived from syngeneic mouse pluripotent stem cells, human iPSC-ECs do not home to the ischemic mouse hindlimb. This lack of functional homing may represent an impairment of interspecies cellular communication or a difference in the differentiation state of the human iPSC-ECs. These results may have important implications in therapeutic delivery of iPSC-ECs.